ISP Technologies BETA BASS - Manual (Page 5)

When properly used, the Decimator should be completely transparent; it should have
no effect on the audio signal other than to remove the background noise. To maximize
the performance of the Decimator, it is necessary to understand both the operation of
the controls and the principles of how the internal circuit operates. After this
understanding, it will be easier to set up the Decimator to suit any application.
Low Level Downward Expansion is performed by use of a high quality voltage
controlled amplifier controlled by an RMS based audio level detection circuit. A second
Time Vector Processing circuit that varies the release response over a 1000 to 1 ratio
controls the release response of the Downward Expander. The release response will be
extremely fast, on the order of 2 milliseconds, if the input signal has a fast decaying
envelope and upwards of 2 seconds if the input signal has a slow decaying signal.
Downward Expansion takes place when the input signal level drops below the preset
threshold. For example: if the threshold is set for 0db and input signal of 0db with
produce no expansion. As the input signal drops below 0db, downward expansion
starts and increases exponentially the farther the input signal drops below the threshold
point. The graph below shows the response of the Expander with a 0db threshold.
To set up the Decimator for proper operation first determine the reference level of the
system that the Decimator will be connected to. Most professional products operate at
a +4dbu reference level. Music equipment typically operates at –10dbu. Once the
proper reference level is determined, set the reference level switch on both channels
accordingly.